IMO rank is a personal thing. I know there has to be a standard, but what is it exactly? I've trained with people who to the casual observer didn't appear to be worthy of their rank, but once you got to know them, that perception changed.
There was a woman who trained at my previous dojo. She was a 3rd dan. She technically could do everything from the sense that she had stuff like kata and kihon memorized. It looked like she was just walking through all the solo stuff. Within her physical limitations (she had some pretty bad arthritis in her knees which seriously limited some of her stances and mobility), she did everything correctly, but there was no speed or power behind it; it looked like she'd just physically memorized the movements and was at the stage where she's getting ready to speed it up and add power. She was proficient in sparring, but nothing noteworthy by any stretch of the imagination. If you'd walk in and watch class, you'd think she bought her rank and nothing more.
She was always the first one in and the last one out. She'd offer to help anyone and everyone at any time (not in a know it all way) and loved it. She had very good insight and tips to make things better. Thinking more about it, she was practically a walking encyclopedia up to her rank, from a mental standpoint.
She always gave it her all, always had a smile on her face while doing everything, and never made excuses. She taught a majority of the kids classes and had a way of getting the best out of them.
IMO she put more into earning those three stripes on her black belt than anyone else in the dojo. Watching her perform wasn't pretty, but she did it to the best of her ability.
If doing the best someone can honestly do combined with all the other stuff she did isn't enough, then what is? At the end of the day, it's only stripes on a belt. The only people who didn't think she was worthy of her rank were the people who didn't know anything about her. This be totally honest, if all I saw was her on promotion day performing the way she does, I wouldn't pass her. And I'd most likely lose a very good student and mentor for other students as a result.
Rank is a personal thing.